A giant magnetoresistance (GMR) element constituted of a multilayer film having a ferromagnetic layer and a nonmagnetic layer, and a tunneling magnetoresistance (TMR) element using an insulating layer (tunnel barrier layer, barrier layer) as a nonmagnetic layer are known as a magnetoresistance effect element. Generally, a TMR element has high element resistance and a high magnetoresistance (MR) ratio compared to a GMR element. Therefore, the TMR element has attracted attention as an element for a magnetic sensor, a high-frequency component, a magnetic head, and a nonvolatile magnetic random-access memory (MRAM).
The MRAM reads and writes data utilizing the characteristic that the element resistance of a TMR element changes when orientations of magnetizations of two ferromagnetic layers sandwiching an insulating layer therebetween change. As a writing method of an MRAM, a writing method utilizing a magnetic field made by a current (magnetization rotation), and a writing method utilizing a spin-transfer torque (STT) caused when a current flows in a lamination direction of a magnetoresistance effect element (magnetization rotation) are known.
A magnetization rotation of a TMR element using an STT is efficient when considered from the viewpoint of efficiency in energy. However, the rotational current density for a magnetization rotation is high. It is desirable that the rotational current density be low from the viewpoint of extending the life of a TMR element. The same applies to a GMR element as well.
Recently, a magnetization rotation utilizing a pure spin current generated through spin orbit interaction as means of reducing a rotational current has attracted attention (for example, Non-Patent Document 1 in I. M. Miron, K. Garello, G Gaudin, PJ. Zermatten, MV. Costache, S. Auffret, S. Bandiera, B. Rodmacq, A. Schuhl, and P. Gambardella, Nature, 476, 189 (2011)). This mechanism has not been sufficiently elucidated. However, it is assumed that a pure spin current caused due to the spin orbit interaction or the Rashba effect at the interface between different materials induces a spin-orbit torque (SOT), and a magnetization rotation is caused. A pure spin current is generated when the same number of electrons of an upward spin and electrons of a downward spin flow in orientations opposite to each other, and a flow of electric charge is offset. Therefore, a current flowing in a magnetoresistance effect element is zero, and an extended life for the magnetoresistance effect element is expected.
On the other hand, it is said that a magnetization rotation using an SOT needs to disrupt the symmetry of a magnetization causing a magnetization rotation, by applying an external magnetic field (for example, Non-Patent Document 2 in S. Fukami, T. Anekawa, C. Zhang, and H. Ohno, Nature Nanotechnology, DOI: 10. 1038/NNANO. 2016. 29). In order to apply an external magnetic field, a generation source for an external magnetic field is required. A generation source for an external magnetic field provided separately outside leads to deterioration in the degree of integration of an integrated circuit including a spin current magnetization rotational element. Therefore, a technique of enabling a magnetization rotation using an SOT without applying an external magnetic field is also being studied.
For example, Non-Patent Document 3 in Guoqiang Yu, et al., Nature Nanotechnology, DOI: 10. 1038/NNANO. 2014. 94 discloses that the symmetry of the intensity of a magnetization collapses due to changing of the oxygen content of an oxide film bonded to a ferromagnetic material causing a magnetization rotation. When the symmetry of the intensity of a magnetization collapses, a magnetization rotation is likely to occur, so that a magnetization rotation using an SOT can be performed even if there is no magnetic field.